I'm not quite sure how it is overrated. The prequels are universally maligned, Jedi's gotten it's share of flack over the past 25 years, and the "expanded universe" productions are generally mediocre and not well reviewed. With the exception of a small selection of games, books, and the original Clone Wars shorts, what exactly has there been positive to say about SW in 30 years?
You can't deny the original film is a classic and one of the most important films ever made, and Empire surpasses it in quality on almost every level. The rest Is a mixed bag, at best. I wouldn't call that overrated.